The subject matter disclosed herein relates to the art of rotary wing aircraft and, more specifically, to rotor systems for rotary wing aircraft.
Lead-lag is the forward and backward in-plane motion of the blades of an articulated rotor. The lead-lag dynamics of rotor blades tend to be very lightly damped because the primary damping force is caused by the drag, which is much lower than the lift forces. Two lead-lag rigid dynamical modes that tend to be under-damped are “regressive” and “progressive” lead-lag modes. The progressive lag mode occurs when the center of mass of the rotor is moving around the shaft in the same direction as the rotor rotation. The regressive lag mode occurs when the center of mass of the rotor is moving in the opposite direction as the rotor rotation. A phenomena known as “ground resonance” occurs when the frequency of the regressive lag mode becomes too close to the frequency of a coupled body-landing gear mode.
To provide sufficient damping for these lead-lag modes, supplementary mechanical dampers are typically used. These mechanical dampers are usually sized to prevent ground resonance. Lead-lag dampers tend to increase rotor system cost and decrease performance because they are complex, heavy, cause high hub drag, and require maintenance.